Networker

Re: [Networker] How to tell how much physical tape is being used?

2007-04-24 16:11:33
Subject: Re: [Networker] How to tell how much physical tape is being used?
From: Doug Brown <Doug.Brown AT ABBOTT DOT COM>
To: NETWORKER AT LISTSERV.TEMPLE DOT EDU
Date: Tue, 24 Apr 2007 15:08:42 -0500

We backup 3.1TB to 3 LTO's in about 5.5 hours.   I don't use the compression in rman, just let legato deal with it.   Recovery has always been there.



George Sinclair <George.Sinclair AT NOAA DOT GOV>
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04/24/2007 03:04 PM
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Re: [Networker] How to tell how much physical tape is being used?





Excellent point, but if that 10 GB is being compressed down to say 5 GB
via the 'compressed' option, for example, then you're only using 5 GB of
tape, but if your rman script isn't using the 'compressed' option, and
you're sending all 10 GB to the drive then the drive is still gonna use
hardware compression, so how do I determine which method actually used
less tape? Maybe it's a toss up?

Is the 'compressed' option recommended in rman scripts with NMO? Should
we be using that option? It certainly compresses things down way small -
almost too small to be believed - but when we recovered from tape,
everything was there. Maybe it's just the data we were playing with, but
I've never seen compression that good. Sheesh! The main draw back I see,
however, is that it doesn't end up creating large enough data streams to
keep the drives streaming. Maybe not such a factor on a smaller test
database (say 10 GB or so) like I was playing with but could be a
problem when dealing with the real thing?

Do you recommend using that 'compressed' option?

Thanks.

George

Doug Brown wrote:
>
> George
>
> Keep in mind too that if you use the incremental functionality of
> RMAN, then only blocks that have changed since the previous level - 1
> will be backed up.   And RMAN only backs up blocks used in the
> database period in a level 0 ( full ) backup.   So if your tablespace
> is sized at 100GB and the objects inside are only using 10GB then
> you're only using 10GB of tape.
>
>
>
> *George Sinclair <George.Sinclair AT NOAA DOT GOV>*
> Sent by: EMC NetWorker discussion <NETWORKER AT LISTSERV.TEMPLE DOT EDU>
>
> 04/24/2007 02:35 PM
> Please respond to
> EMC NetWorker discussion <NETWORKER AT LISTSERV.TEMPLE DOT EDU>; Please
> respond to
> George Sinclair <George.Sinclair AT NOAA DOT GOV>
>
>
>                  
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>                  
> Subject
>                  [Networker] How to tell how much physical tape is being used?
>
>
>
>                  
>
>
>
>
>
> Is there a way to determine how much physical tape space is being used
> by a backup?
>
> For example, lets suppose I run an Oracle backup using RMAN with NMO,
> and the RMAN script uses Oracle's compression feature (compressed), and
> let's say the backup is a level full and creates 5 save sets at around
> 200-300 MB each (each save set has say 4-6 files each). Next, I run the
> same backup, but this time I don't use the 'compressed' option in the
> RMAN script, and maybe I get 5 save sets again, but this time they're
> much larger, say 1 GB each. I recover everything in both examples, and
> the recovered database is exactly the same as far as the number of files
> and their sizes. Well, hardware compression is enabled on the drives, so
> the data is getting compressed both times, and in the second example,
> while I may be backing up approx. 5 GB of data, I'm probably not using 5
> GB worth of tape space due to hardware compression, so it is possible
> that both examples result in the same amount of physical tape space
> being used? Maybe?
>
> Is there a way to tell which method is actually using more tape or if
> they're close?
>
> I can query for the 'mediafile' numbers for the save sets, and I notice
> that they always start 2 beyond the previous one, but a given saveset
> could be of any size so this doesn't really tell me how much tape is
> being used, right?
>
> Here's why I ask such a goofy (stupid?) question. OK, we ran this Oracle
> backup (level full) with the 'compressed' option, and we noticed that
> the backup size was very small (kinda nice!), but as a result, the drive
> speeds were very slow. This is not surprising given that we probably
> were underfeeding the drives since the client was sending less data due
> to the Oracle compression. Next, we run the same thing but without the
> 'compressed' option, and now the drives scream (again, not surprising
> given that the client now has more data to send), but the backup sizes
> were way larger. Overall, however, the backup completion times were
> reasonably similar. I'm wondering if maybe in the second example that
> because the data was not already compressed that the drives shrunk it
> down and that maybe it's not really taking up any more space on the tape
> than the same data in the first run. We recovered both sets, and the
> total number of recovered database files and their sizes are the same in
> both cases.  How can I determine, therefore, which method used less tape?
>
> Thanks.
>
> George
>
> --
> George Sinclair - NOAA/NESDIS/National Oceanographic Data Center
> SSMC3 4th Floor Rm 4145       | Voice: (301) 713-3284 x210
> 1315 East West Highway        | Fax:   (301) 713-3301
> Silver Spring, MD 20910-3282  | Web Site:  http://www.nodc.noaa.gov/
> - Any opinions expressed in this message are NOT those of the US Govt. -
>
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--
George Sinclair - NOAA/NESDIS/National Oceanographic Data Center
SSMC3 4th Floor Rm 4145       | Voice: (301) 713-3284 x210
1315 East West Highway        | Fax:   (301) 713-3301
Silver Spring, MD 20910-3282  | Web Site:  http://www.nodc.noaa.gov/
- Any opinions expressed in this message are NOT those of the US Govt. -

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